1. Field of the Invention
The present invention relates to a rotary indexing apparatus for indexing a rotary member such as a turntable of a machine tool.
2. Discussion of the Related Art
Japanese Utility Model Publication (kokoku) No. 8-10505 discloses a direct-drive-type rotary indexing table which can be rotated for indexing with no vertical movement of the table.
However, the complex structure of the conventional rotary indexing table increases production costs thereof and makes reducing the overall size difficult. The conventional rotary indexing table has a clamp mechanism composed of a cylinder disposed under the table in the vicinity of the rotation center of the table, and a piston which is pressed against the bottom surface of the table by the pressure of operation fluid supplied to the cylinder. Therefore, there exists a limit on the clamping force generated by the clamp mechanism.
Especially, when the overall size is reduced, the clamping force decreases due to a decrease in the diameter of the cylinder. Although this problem can be solved by increasing the pressure of operation fluid supplied to the cylinder, there arises a possibility that the cylinder, the piston, bolts, an o-ring, and the like are damaged.
In addition, since the cylinder or the piston is in frictional engagement with the bottom surface of the table, the surfaces involved in the frictional engagement are subjected to wear. Therefore, such surfaces must be lubricated.